1. Field of the Invention
The invention relates to a process for the catalytic hydrogenation of the C--C double bond of .alpha.,.beta.-unsaturated ketones, which have at least one substituent containing bonded halogen, to give the corresponding saturated ketones. This hydrogenation is carried out on Ni-containing catalysts and in the presence of an organic sulphur compound.
2. Description of the related Art
In the selective hydrogenation of C.dbd.C bonds in the presence of other functional groups, the lability of halogen substituents, for example, in particular in basic medium, has to be taken into account; even fluorine is cleavable in the presence of nickel (Houben-Weyl, Methoden [Methods], 4th edition, vol. 4/1c (1980), 155). Even with the simultaneous presence of carbonyl groups, in this case particularly with .alpha.,.beta.-unsaturated ketones, undesired hydrogenation of the oxo group has to be taken into account (Houben-Weyl, loc. cit., p. 162); this undesired reaction is observed more strongly with Ni catalysts than with Pd catalysts (P. Rylander, Catalytic Hydrogenation in Organic Synthesis 1979, p. 51).
Even in the catalytic hydrogenation of aromatic nitro compounds to give the respective arylamines, cleavage of simultaneously present, aromatically bonded halogen is observed. In order to suppress such a cleavage of halogen, the noble metal catalysts employed for such hydrogenations were modified. To this end, a procedure can be used in which a separately prepared modified catalyst is employed or in which a modifying agent is added to the reaction mixture as such. Thus, sulphides of the noble metals were employed in GB No. 1,064,959; DE-OS (German Published Specification) No. (2,105,780 describes a Pt/C contact with Na.sub.2 SO.sub.3 doping; DE-OS (German Published Specification) No. 2,150,220 describes noble metal/activated carbon/sulphoxide catalysts. DE-AS (German Published Specification) No. 2,549,900 describes the hydrogenation of chloro-nitro aromatic compounds using noble metal catalysts and with the addition of thioethers as modifying agents.
The use of modifying agents such as those described is always combined with a decrease in the catalyst activity which frequently leads to relatively long hydrogenation times or requires the use of more severe reaction conditions. For the unproblematic hydrogenation of nitro compounds, the reduced catalyst activity is in fact always completely sufficient, which was not to be expected for the hydrogenation of C.dbd.C double bonds.
With complicated hydrogenation problems, such as, for example, the hydrogenation of a C.dbd.C double bond with the retention of an oxo group and the avoidance of hydrogenolytic cleavage of halogen, as in the present case, a non-uniform course of the hydrogenation thus had to be taken into account, in particular since with .alpha.,.beta.-unsaturated ketones, frequently either an undesired hydrogenation of the carbonyl group is observed or in order to avoid this undesired reaction incomplete hydrogenation of the double bond has to be taken into account.